The present invention relates to compounds which modify the molecular weight of polymerized lactams. More specifically, the present invention relates to the use of compounds which allows anionic polymerization of lactams to proceed at a normal rate and yet inhibits coupling and/or chain transfer which generally produce high molecular weight and/or gelled polylactams.
Heretofore, the anionic polymerization of lactams produced polylactams often having much higher molecular weights than that expected from calculations based upon the elements of lactam monomer and anionic initiators. Generally, the much higher molecular weight has been attributed to branching reactions such as between an amide ion and an imide chain end which produce a coupled site. This reaction often resulted in very high molecular weight products and/or gels, especially with longer polymerization time periods and hence altered the rheology of the polylactam. Since the range of molecular weights of polylactams would vary from batch to batch depending upon the amount of branching or coupling, processing problems were often encountered in situations wherever rheology considerations tend to be important such as in fiber making, spinning operations and often in molding.
In an article entitled "Initiated Polymerization of Caprolactam: Molecular Weight Control" by E. H. Mottus, R. N. Hedrick and J. M. Butler, American Chemical Society POlymer Preprints, 9(1) Page 390 (1968), aliphatic, cycloaliphatic and aromatic amines and amides were added to anionically polymerizing lactam systems to react with the potential coupling sites thereby reducing the concentration of such sites sufficiently to prevent the undesirable branching reaction. However, the reaction of amides with the potential coupling sites generally resulted in chain termination and generation of new chains while amines resulted in chain termination. Thus, the overall effect was the production of a polylactam which generally had molecular weights much below the calculated value due to the chainn termination and/or chain transfer reactions. Polymers produced utilizing amine and amide modifiers thus go to a lower conversion and are less viscous.